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Rigid PVC use in Blackwater marine systems?

May 28, 2018
5
Beneteau Oceanis 38 San Francisco
Peggie, I noted that Sail Magazine just published an article whose author advocates the use of rigid home-grade PVC plumbing when modifying marine blackwater systems [see: Know-how: Modify a Blackwater System ]. What are your thoughts on using this type of material? Thanks.
 
Dec 2, 1997
7,465
- - LIttle Rock
Rigid pvc--aka "hard pipe" is only recommended for long STRAIGHT runs 'cuz any bends that are greater than the pipe wants to bend require cutting the pipe and inserting inline radius fittings, every one of which is a fitting that can trap waste and TP, and where sea water minerals and salt can build up. More than one or two of those creates more problems than it solves. That hard PVC is a lot cheaper than top quality odor permeation proof hose is its only advantage.

Edit: I just read the article. He could have eliminated both the 45 and the 90 in the first photo by simply moving the inlet fitting on the tank to the top of the tank (apparently he's never heard of the Uniseal, which would have made this an easy job). I could only see enough of the tank vent line to see the two 90s in it and it also appeared to be the "standard" 5/8". So while he may have eliminated permeated hoses as a source of odor INside the boat, it's unlikely that what comes out the tank vent will be odorless. And there were several other things that he made a lot more complex than they needed to be.

--Peggie
 
Last edited:
Jun 11, 2004
843
Oday 31 Redondo Beach
I just read the article. He could have eliminated both the 45 and the 90 in the first photo by simply moving the inlet fitting on the tank to the top of the tank (apparently he's never heard of the Uniseal, which would have made this an easy job).
--Peggie
Peggie:
What would be your recommended best way to plug the old hole?
Thanks!
 
Dec 2, 1997
7,465
- - LIttle Rock
A threaded plug wrapped in plenty of teflon tape will seal any female threaded tank fitting securely. You should have no trouble finding a 1.5" threaded plug in the plumbing section of any decent hardware store.
 
Aug 31, 2017
102
Marshall 22 Falmouth, ME
I think Don Casey makes good points about the use of PVC- check out this old boat. In a nutshell you are replacing a product impervious to permeation, vibration and impact damage, which can bend and requires 2 connections (quality hose); with a product impervious to permeation that can crack from vibration and impact damage (pvc) that also introduces a myriad of connections (all potential failure or debris catching points) and requires precise measuring and mounting and adds the "fun" of fitting straight pipes into a curved shape.

To me one length of Peggie approved hose seems like such an elegantly simple solution it's a no-brainer. To each his or her own though.
 
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Aug 31, 2017
102
Marshall 22 Falmouth, ME
Awww shucks. Coming from such a knowledgeable and intelligent person as you Peggie I take that as a real compliment. :)